Method of concentrating kryptonxenon



Dec. 6, 1960 w. DENNIS 2,952,868

METHOD OF CONCENTRATING KRYPTON-XENON Filed Feb. 17, 1956 INVENTORWOLCOTT DENN I'S W W 7/ ATTORNEYS United States Patent I METHOD OFCONCENTRATING KRYPTON- XENON Wolcott Dennis, Union, N.J., assignor toAir Reduction Company, Incorporated Filed Feb. 17, 1956, Ser. No.566,308

13 Claims. (Cl. 62-42) This invention relates to the separation of airfor the purpose of obtaining a krypton-xenon fraction and moreparticularly concerns the production of a high-purity krypton-xenonfraction comprising 1% K-X in essentially liquid oxygen.

The letter symbols K, X, and O are sometimes used hereinafter forconvenience in designating krypton, xenon and oxygen respectively.Similarly, the designation LQO is used for liquid oxygen. Use of thesesymbols together identifies mixtures thereof, such as K-X-O for amixture of krypton, xenon and oxygen, K-X for a mixture of krypton andxenon, etc.

Much has been written and proposed recently concerning the excellentprospects for K-X in filling incandescent lamps and in other uses. Ithas been suggested that oxygen production will become a byproduct of theproduction of krypton or xenon or a mixture of the two.

The primary object of the present invention is to produce a high-purityK-X fraction in LQO. A further object is a method for the production ofhigh-purity liquid oxygen and a crude K-X fraction which is converted tohigh-purity krypton and xenon. An additional object is a method forobtaining a 1% K-X in liquid oxygen (LQO) from a crude K-X fractionwhich contains about 100 parts per milllion (p.p.m.) o-f K-X in a purgeliquid.

The preferred embodiment of the present invention accomplishes the aboveobjects by warming a crude K-X stream of oxygen, hydrocarbons, krypton,xenon, argon, and nitrogen, passing said warmed stream through a devicewhich converts the hydrocarbons (HC) to CO and H and consequently adesensitized K-X stream. Thereafter this desensitized stream is cooledto about 70 F. whereby the H 0 is separated and a substantiallydewatered K-X stream results. This K-X stream is then passed throughreversing heat exchangers so that the CO and residual H O are depositedon the heat exchange surfaces and then flushed out by a suitable pickupstream. Next, the so-treated K-X stream is fractionated with theassistance of certain relatively warm and cold fluids so that a liquidproduct containing about 1% KX in LQO and an effluent of argon, oxygen,and nitrogen are obtained. Thereafter, it is preferred to vaporize the1% K-X in essentially LQO and to remove any residual traces ofhydrocarbons.

The accomplishment of the above objects and other objects, along withthe features and advantages of the present invention, will be betterunderstood by reference to the following description and theaccompanying drawing of the preferred embodiment of the presentinvention.

It is to be understood that in the present application all references totemperature are by degress Fahrenheit and all references to pressure areby pounds per square inch absolute (p.s.i.a.) The use of the letter Vmeans vapor state and the use of the letter L 2,962,868 Patented Dec. 6,1960 means liquid state. The flows (quantities: before V or L) arestandard cubic feet of gas per minute (s.c.f.m.).

For the sake of clarifying and simplifying the drawing, various wellknown components which are well understood to those skilled in the arthave been shown schematically and identified in certain instances bydescriptive symbols. Thus, in the drawings, the following symbols willbe understood to designate conventional and commonly understoodinstrumentation and apparatus as follows: T designates a temperaturegauge; SV identifies a safety valve; SH, a safety head; FR, a. flowrecorder instrument; V, a valve; PRC, a pressure regulator controllerand F. a flow meter.

In the drawing, a liquid consisting essentially of 40% oxygen, 30 p.p.m.HC, p.p.m. K-X and the remainder nitrogen and traces of argon withperhaps a 30- 40 p.p.m. CO flows in pipe 11 at the left-hand side of thedrawing. This liquid is obtained from the air separation processdisclosed in US. application S. N. 326,985 now US. Patent No. 2,762,208by the inventor of the present invention. This copending patentapplication teaches the step of scrubbing incoming air withoxygenenriched liquid air in a liquid oxygen producing plant so that apurge liquid or crude K-X stream constituting about 1% of the incomingair and consisting essentially of oxygen, argon, K-X, hydrocarbons, andnitrogen is obtained. The incoming air flow to the scrubber is, forexample, about 5,284V+216L at about 94# and about 277". This air isscrubbed in the scrubber portion of a nitrogen column containing about10 plates by 316L of oxygen-enriched air and the liquid in the bottom ofthe scrubber section is boiled by a composite stream of nitrogen at 270and l60#. Under the above-described flow conditions, a K-X purge ofabout 50-54L at 277 and 94# is continually removed. The refluxproportion is 316L (descending liquid) to 5762V (ascending vapors). Inthe drawing, a purge liquid containing a krypton-xenon fraction which isdelivered in the line 11, is: shown taken from the scrubber section S ofa nitrogen column F of a conventional air rectification system, theincoming air stream to the column being shown at A. Liquid reflux forthe nitrogen column may be supplied in any conventional manner such, forexample, by introduction of liquid nitrogen at N and the scrubbersection may be reboiled by circulating a nitrogen stream as abovedescribed through a reboiler shown at R, such operation of a scrubberbeing well understood to those skilled in the art. It is to beappreciated that, when a plant is built to produce LQO, there arespecial considerations involved if it is also desired to recover thep.p.m. of K-X.

The above-described K-X purge liquid containing about 100 p.p.m. K-Xenters the apparatus shown on the accompanying drawing by means ofconduit 11 (as above mentioned) and then passes through heat exchanger13. In heat exchanger 13, this K-X purge is converted to vapors at 60and 90#. From heat exchanger 13, the K-X stream moves through pipe 15 toexchanger 17 in which it is preferably further warmed to about 525. Thisfurther warmed K-X stream at about 8l# flows through pipe 19 to purgegas combustion furnace 21 wherein the hydrocarbons are converted to COand H 0 and a desensitized K-X stream is formed. This desensitizedstream containing CO and H 0 and perhaps about 1 p.p.m. HC in some casesthen returns to heat exchanger 17 wherein it is cooled to and leavesthis exchanger at about 65#. The desensitized K-X stream then movesthrough pipe 23 to the water-cooled was stream leaves the separator 27through pipe 31 and moves to reversing heat exchangers 33 which arecontrolled by the four reversing valves 35. These valves 35 automatically provide for directing the dewatered KX stream from pipe 31alternately into one of the two passages of heat exchanger 33. Fromreversing exchanger 33 the dewatered KX stream passes to a secondsection of reversing exchangers 37 having exit control valves 39. Thesevalves 39, together with valves 35, complete the controls necessary toalternately pass for about fifteen minutes the KX stream through oneside of exchangers 33 and 37 while a pickup gas (55V at about 310) ispassing through the other sides of these exchangers and then foralternating these flow paths. In reversing exchangers 33 and 37, thedewatered KX stream is sufficiently refrigerated so that any CO thereinand any residual traces of H are deposited as solids in these heatexchangers. This results in a purified KX stream at about -295 and 59#.This purified KX stream with the valves positioned as shown in thedrawing leaves the reversing heat exchangers through pipe 41 and flowsthrough expansion valve 43 to the fractionating or rectification column45. The purified KX stream leaves ex pansion valve 43 at about 35 In therectification column 45, a pressure of about 35# is maintained. Column45 basically consists of a stripper section 47, lower rectificationsection 49, a re flux condenser 51 and a heater coil 53 in heatexchanger relation with the bowl 55 of the column. In column 45 a KXstream of 50V containing oxygen, KX, nitrogen and traces of argon isfractionated in such a manner that a liquid fraction is produced,containing about 1% KX in LQO at about 280 and about 35# andconstituting 1L. Essentially complete recovery of all of the KX enteringthe apparatus is thus achieved. It will be recalled that the initialconcentration of KX in pipe 11 was about 100 ppm. while the finalconcentration is 10,000 ppm. The eflluent from column 45 is at about 293and 34#. The larger sized stripper section of column 45 contains 8 traysand the lower rectification section also contains 8 trays. Therespective proportion of descending liquid to ascending vapors are to 54(upper) and 5 to 4 (lower). The liquid fed to the reflux condenserpreferably is a fluid at about 315. The fluid actually used is liquidnitrogen at about -3l5 and 20# being 5.8L+.2V. The fluid which boils theliquid in the bowl 55 preferably is at 272". The fluid which is actuallyused is a recycle nitrogen stream at 270 and 2500# and being 200V.

The KX liquid withdrawn from the column 45 by means of pipe 61preferably passes to water-warmed coil 63 because this liquid fractionin some cases may contain residual traces of hydrocarbons. Thus, it isgreatly preferred that this liquid stream (1% KX in LQO 1L, 50, 34#) asit exists after passing through coil 63 is passed through pipe 65 to asecond combustion furnace 67. In combustion chamber 67, any residualtrace of hydrocarbons is eliminated by conversion to H 0 and C0 Theso-treated KX stream, as a vapor at 150, is next cooled in water-cooledcoil 71 to about 70. Thereafter it passes alternately through productdecarbonizers 73 and product driers 75 wherein the CO and H 0 areremoved. The decarbonized and dried, very purified, KX stream is passedthrough pipe 77 to heat exchanger 79 wherein it is liquefied by heatexchange with a suitable fluid. The liquefied KX fraction is madebecause in some plants there are no means for further separating the KXand it is necessary to transport the 1% KX to a separation facility.Since often this separation facility is some distance from the KXproducing plant, it is greatly preferred to ship it as a liquid. Thus,the liquid leaving heat exchanger 79 moves through pipe 81 to aconventional Dewar flask 83 which is then shipped to a distant KXseparation plant. ,It is to be understood that the gaseous KX fractionleaving combustion furnace 67 decarbonizers and driers can be separatedinto pure KX locally. It is also to be understood that in many cases thefinal purification may not be required and that the product leavingcolumn 45 would be the end KX product like that collected in the flasks.

Referring now to the fluids which condition the crude KX fraction whichentered at pipe 11, it can be seen that heat exchanger 13 has two suchfluids flowing in opposite directions thereth'rough. The fluid passingthrough the center path enters said exchanger 13 as nitrogen vapor(200V) at 70 and 2500# after passing through filter 101. for foreignmatter removal in pipe 103. This nitrogen stream preferably is part ofthe closed recycle stream disclosed in the above-mentioned copendingpatent application. It leaves exchanger 13 at about 272 and flowsthrough pipe to coil 107 in heat exchange with the bowl of column 45.This nitro gen stream, after effecting the boiling of liquid in thebottom of column 45 leaves coil 107 through pipe 109 at about 270 and160#.

The fluid which is supplied by pipe 111 to reflux con denser 51preferably is liquid nitrogen (5.8L+0.2V) at about -3l5-- and 20#. Thevaporized nitrogen leaving reflux condenser 51 by means of pipe 113 isused after a slight pressure reduction by valve 39, along with Wastenitrogen (55V) entering via pipe 115 as a pickup gas- (at least about10% more than the incoming KX flow) for the reversing exchangers 33 and37. This pickup gas sublimes the CO and H 0 deposited in the reversingheat exchangers by the purified KX stream. Thereafter this pickup streamis sent to Waste or discharged to atmosphere. The waste gas (61V) movingthrough pipe 115 is at about 310 and 17#.

The other fluid used in the process, other than the water used to coolcoils 25, 63, and 71, is the fluid used to liquefy the very purified K-Xfraction in heat exchanger 79. This fluid is effluent which leaves thetop of reflux condenser 51 through pipe 121 and is comprised ofnitrogen, oxygen, and argon. This stream (49V) in pipe 121 is at about-293 and 34#. After liquefying the very purified KX stream in exchanger79, this eflluent stream moves through pipe 123 as purged gas residue.This purged gas (49V) residue is at about :278 and'28#.

The combustion furnace 21 preferably contains a palladium on aluminacatalyst such as disclosed in the Rosen-blatt US. Patent No. 2,582,885,which may, for example, be in granular form such as is indicated by thereference C designating a bed of the catalyst packed in a reactor tubesection 21a of the furnace. It is heated to 600700 and the gas leaves atabout 600. In some instances, it may be desirable to use an Inconeltube- (78% Ni, 7% Fe and 14% Cr). This catalyst tube preferably isheated to about 15001600. The gas would enter at about 1425 and leave atabout 1500*. A silver on alumina catalyst operated at about 1300" hasalso proved effective. Combustion furnace 67 preferably contains theabove-mentioned palladium on alumina catalyst and preferably is precededby a conventional flash arrester 133 to prevent blow-back to the column.Product decarbonizers 73 preferably contain soda lime (8 x 16 mesh).silica gel.

It is to be understood that the gas which may escape during the fillingor storage of Dewar containers 83 can be vented to atmosphere or savedin a gas holder. It is also to be understood that pipe 81 coulddischarge into a large vacuum powder storage container or the like or;

into a. railway tank car or tractor trailer having a liquefied gascontainer, all preferably refrigerated. Expansion valve 43isautomatically controlled by conventional air-operated pressureregulating control 141. Two

Product driers 75 preferably contain liquid level controls 143 areshownoperatively connect d to the reflux condenser 51 and the columnbowl 55.

The operation of the apparatus and the steps of the process are believedto be apparent, to those skilled in the art, from the foregoingdescription. Some of the noteworthy features which can be againmentioned are the arrangement for purifying the K-X stream after itpasses through the purged gas combustion furnace by means of thereversing exchangers in which the greater nitrogen flow for picking updeposited CO is v provided; another such feature is the purification ofthe '1% K-X-O stream by means of a combustion furnace "and then thesecond liquefaction of the highly purified stream; of note also is theparticular manner in which the rectification column is operated since itis refluxed by "a fluid at 315 and is suitably boiled by an externalfluid and it has the very eflicient reflux proportions be- '=tweendescending liquids and ascending vapors. The agents attributable to theabove-mentioned features are believed to be obvious, for example, aneificient primary l'purification step is provided, a substantially 100%recovery of K-X is provided, and a continual purge of the column andpurification of the final 1% K-X in oxygen is also provided.

.It is to be understood that the person skilled in the :-art can makechanges in the above-described preferred embodiment without departingfrom the invention as :defined in the following claims.

I claim:

1. A method of concentrating krypton and xenon in *oxygen comprisingwarming a crude krypton-xenon stream of oxygen, hydrocarbons, krypton,xenon, argon, .:and nitrogen, passing said warmed stream through a:combustion furnace containing a palladium catalyst at :about 600 F. to700 F. whereby hydrocarbons are con- Verted to CO and H 0 and adesensitized krypton- :xeuon stream is formed, removing said CO and H 0from said desensitized krypton-xenon stream by cooling :so that said COand H 0 are deposited as solids whereby :a purified krypton-xenon streamis formed, fractionating :said purified krypton-xenon stream byrefluxing with the raid of a fluid at about -315 F. and by boiling withthe aid of a fluid at about -272 F. whereby said purified krypton-xenonstream is separated into a liquid fraction comprised of krypton-xenon inliquid oxygen.

2. The method according to claim 1 and further including the step ofconverting said liquid fraction into a gas and passing it through acombustion furnace so residual traces of hydrocarbons are removed and avery purified krypton-xenon-oxygen stream results.

3; A method of concentrating krypton and xenon in liquid oxygencomprising warming a crude liquid kryptonxenon stream of oxygen,hydrocarbons, krypton, xenon, argon, and nitrogen at about 90 p.s.i.a.to about 60 F., further warming said stream to about 525 F., passingsaid further warmed stream through a combustion furnace containing apalladium alumina catalyst at about 600 F.-700 F. whereby hydrocarbonsare converted to CO and H 0 and a desensitized krypton-xenon stream isformed, cooling said desensitized krypton-xenon stream to about +70 F.and separating H O therefrom to form a dewatered krypton-xenon stream,removing said CO and H 0 from said dewatered krypton-xenon stream bycooling so that said CO and H 0 are deposited as solids whereby apurified krypton-xenon stream at about -295 F. is formed, fractionatingsaid purified krypton-xenon stream at about 35 p.s.i.a. by refluxingwith the aid of a fluid at about 315 F. and about 20 p.s.i.a. and byboiling with the aid of another fluid at about 272 F. whereby saidpurified krypton-xenon stream is separated into a liquid fractioncomprised of 1% krypton-xenon in liquid oxygen at about -281 F.

4. The method according to claim 3 and further including the steps ofconverting said liquid fraction into a gas and passing it through acombustion furnace so residual traces of hydrocarbons are removed and avery purified krypton-xenon-oxygen stream results, and then liquefyingsaid krypton-xenon-oxygen stream by refrigeration derived from theeflluent from said fractionating step.

5. A method of concentrating krypton. and xenon in oxygen comprisingwarming a crude krypton-xenon stream of oxygen, hydrocarbons, krypton,xenon, argon, and nitrogen, passing said warmed stream through acombustion furnace whereby hydrocarbons are converted to CO and H 0 anda desensitized krypton-xenon stream is formed, cooling said desensitizedkrypton-xenon stream to about 70 F. and separating H O therefrom to forma dewatered krypton-xenon stream, removing said CO and residual H O fromsaid dewatered krypton-xenon stream by cooling in such a manner thatsaid CO and H 0 are deposited as solids whereby a purified krypton-xenonstream is formed, fractionating said purified kryptonxenon stream byrefluxing with the aid of a fluid at about -3l5 F. and by boiling withthe aid of a fluid at about 272 F. whereby said purified krypton-xenonstream is separated into a liquid fraction comprised of kryptonxenon inliquid oxygen, and converting said liquid fraction into a gas andpassing it through a combustion furnace so that residual traces, if any,of hydrocarbons are removed and a very purified krypton-xenon-oxygenstream results.

6. A method of concentrating krypton and xenon in liquid oxygencomprising warming a crude liquid kryptonxenon stream of oxygen,hydrocarbons, krypton, xenon, argon, and nitrogen at about p.s.i.a.,passing said warmed stream into contact with a heated catalyst wherebyhydrocarbons are converted to CO and H 0 and a desensitizedkrypton-xenon stream is formed, removing said CO and H 0 from saiddesensitized krypton-xenon stream by cooling in reversing heatexchangers on about fifteen-minute cycle so that said CO and H 0 aredeposited as solids whereby a purified krypton-xenon stream at about 295F. is formed, fractionating said purified krypton-Xenon stream into aliquid fraction containing about 1% krypton-xenon in liquid oxygen andan efllulent containing all of the nitrogen of said crude krypton-xenonstream, said fractionation being done in an upper zone in which theproportion of descending liquid to ascending vapors is about 5 to 54 andthe reflux fluid temperature is about -3l5 F. and in a lower zone inwhich the proportion of descending liquid to ascending vapors is 5 to 4and the boiling fluid temperature is -272 F.

7. The method of fractionating air to obtain a high purity liquid oxygenand an enriched, substantially pure krypton-xenon-oxygen mixture in theorder of about 1% of said krypton-xenon in oxygen, as a by-product,which comprises scrubbing the incoming air to be fractionated withliquefied oxygen-enriched air, to form a gaseous fraction and a crudekrypton-xenon liquid fraction amounting to about 1% of the incoming airand containing about 0.01% concentration of krypton-xenon together withoxygen, nitrogen, argon and hydrocarbons, separating said crude liquidfraction from said gaseous fraction, warming and passing said crudeliquid fraction through a combustion furnace containing a palladiumcatalyst at about 600 F. to 700 F. to convert the hydrocarbons to CO andH 0 and form a desensitized krypton-xenon bearing stream, removing saidCO and H 0 from said desensitized krypton-xenon stream Whereby apurified krypton-xenon bearing stream is formed, fractionating saidpurified krypton-xenon bearing stream, and removing the desired highpurity krypton-xenon enriched product as a liquid from saidfractionation.

8. A method of concentrating krypton and xenon in oxygen comprisingwarming a crude krypton-xenon stream containing oxygen, hydrocarbons,krypton, xenon, argon and nitrogen, passing said warmed, crudekryptonxenon stream through a catalytic furnace reactor wherein saidhydrocarbons are converted to CO and H to form a desensitized, crude,krypton-xenon stream, removing the H 0 and CO formed in said furnacefrom said desensitized stream, cooling said desensitized stream by heatexchange with a relatively cold nitrogen vapor stream, delivering saidcooled, desensitized krypton-xenon stream to a rectification columnwherein said desensitized stream is separated into a gaseous fractionsubstantially free of krypton and xenon which is removed at the top ofsaid column and a substantially pure kryptonxenon-oxygen liquid fractionwhich is collected at the bottom of said column, condensing vapor toproduce liquid reflux at the top of said column by indirect heatexchange with liquid nitrogen and delivering said liquid nitrogen whichis vaporized in furnishing said reflux liquid for use in cooling saiddensensitized kryptonxenon stream.

9. A method of concentrating krypton and xenon in oxygen according toclaim 8 wherein said substantially pure krypton-xenon-oxygen liquidfraction is warmed, passed through a catalytic reactor furnace toconvert any residual hydrocarbons to water and carbon dioxide, removingthe carbon dioxide and water so formed and cooling the thus furtherpurified krypton-xenon stream by heat exchange with the gaseous fractionseparated in said rectification column and effecting the liquefaction ofsaid further purified stream.

10. A method of concentrating krypton and xenon in oxygen according toclaim 8 wherein said crude kryptonxenon stream is warmed by heatexchange with a relatively warm nitrogen vapor stream and saidrelatively warm nitrogen vapor stream is then passed through reboilercoil means at the bottom of said rectification column to produce refluxvapor therein.

11. A method of concentrating krypton and xenon in oxygen comprisingwarming a crude krypton-xenon stream of oxygen, hydrocarbon, krypton,xenon, argon and nitrogne, passing said warmed, crude krypton-xenonstream through a catalytic reactor furnace wherein said hydrocarbons areconverted to CO and H 0, to form a desensitized, crude krypton-xenonstream, passing said desensitized stream through a flow passage of areversing exchanger, cooled by a relatively cold nitrogen vapor streamin an adjacent flow passage, to cool said desensitized stream and removethe H 0 and CO formed in said furnace as solidified deposits, deliveringthe resulting cooled, desensitized krypton-xenon stream to a rectification column, wherein said desensitized stream is separated to form asubstantially pure krypton-xenonoxygen liquid fraction and a gaseousfraction substantially free of krypton and xenon, producing liquidreflux for said column by indirectly condensing a portion of the vaporsat the top of said column with liquid nitrogen, delivering the nitrogenvapors resulting therefrom to said reversing exchanger for use incooling said desensitized krypton-xenon stream and periodicallyreversing the flow passages of said desensitized kryptonxenon stream andsaid nitrogen vapor stream to remove solids deposited in said exchangerfrom said desensitized krypton-xenon stream.

12. The method of concentrating krypton and xenon in oxygen comprisingwarming a crude krypton-xenon stream containing, along with the kryptonand xenon constituent, amounts of oxygen and hydrocarbons, passing saidwarm stream through a combustion furnace containing a palladium catalystat about 600 F. to 700 F.

whereby the hydrocarbon constituent is converted to CO and H 0 and adesensitized krypton-xenon stream is formed, passing said desensitizedkrypton-xenon stream through a reversing exchanger in counterflowcooling relation with a stream of cold nitrogen vapor so as toeffectively deposit the carbon dioxide and H 0 content of saiddesensitized stream as solids in said exchanger, said cold nitrogenvapor being derived from a gaseous effluent separated from the liquidfraction of a partial condensation of air, intermittently reversing andalternating the flows of said desensitized krypton-xenon stream and saidcold nitrogen vapor in said reversing exchanger and delivering saidnitrogen vapor in an amount which is at least about 10% larger than theflow of said desensitized stream so as to effectively periodically purgethe deposited carbon dioxide and water solids, at least partiallyliquefying and fractionating said purified krypton-xenon stream derivedfrom said reversing exchanger and obtaining therefrom an enriched liquidfraction containing krypton and xenon in liquid oxygen.

13. The method of fractionating air to obtain a high purity liquidoxygen and an enriched, substantially pure krypton-xenon-oxygen mixtureas a by-product, which comprises providing a separate nitrogen recyclefor producing refrigeration for the air rectification, cooling an airstream to be rectified by indirect heat exchange with said recyclenitrogen, scrubbing the cool air stream with liquefied oxygen enrichedair to form a gaseous fraction which is subsequently rectified toproduce separate oxygen and nitrogen rectification products and a crudekrypton-xenon liquid fraction amounting to about 1% of the incoming airand containing about 001% concentration of krypton-xenon together withoxygen, nitrogen, argon and hydrocarbons, separating said crude liquidfraction from said gaseous fraction, warming and passing said crudeliquid fraction through a combustion furnace to convert the hydrocarbonsto CO and H 0 and form a desensitized krypton-xenon stream, removingsaid CO and H 0 from said desensitized krypton-xenon stream to form apurified krypton-xenon stream, rectifying said purified krypton-xenonstream in a rectification column wherein said stream is at leastpartially liquefied, vaporizing at least a portion of the liquidcollected at the bottom of said column by heat exchange with arelatively warm stream of said recycle nitrogen and removing the desiredhigh purity krypton-xenon enriched product as a liquid from saidrectification column.

References Cited in the file of this patent UNITED STATES PATENTS2,007,116 Walker July 2, 1935 2,032,925 Ferguson Mar. 3, 1936 2,060,940Kahle Nov. 17, 1936 2,433,536 Van Nuys M Dec. 30, 1947 2,527,623 Fauseket a1. Oct. 31, 1950 2,582,885 Rosenblatt Jan. 15, 1952 2,650,482 LoboSept. 1, 1953 2,664,719 Rice Jan. 5, 1954 2,688,238 Schilling Sept. 7,1954 2,793,507 Hnilicka May 28, 1957 2,793,511 Bonnaud May 28, 1957OTHER REFERENCES The Separation of Gases, second edition (Ruhemann),published by Oxford University Press (London),

1949, pages 86-88, 183-185, and 228236 are relied on.

8. A METHOD OF CONCENTRATING KRYPTON AND XENON IN OXYGEN COMPRISINGWARMING A CRUDE KRYPTON-XENON STREAM CONTAINING OXYGEN, HYDROCARBONS,KRYPTON, XENON ARGON AND NITROGEN, PASSING SAID WARMED, CRUDEKRYPTONXENON STREAM THROUGH A CATALYTIC FURNACE REACTOR WHEREIN SAIDHYDROCARBONS ARE CONVERTED TO CO2 AND H2O TO FORM A DESENSITIZED, CRUDE,KRYPTON-XENON STREAM REMOVING THE H2O AND CO2 FROMED IN SAID FURNACESFROM SAID DESENSITIZED STREAM, COOLING SAID DESENSITIZED STREAM BY HEATEXCHANGE WITH A RELATIVELY COLD NITROGEN VAPOR STREAM, DELIVERING SAIDCOOLED, DESENSITIZED KRYPTON-XENON STREAM TO A RECTIFICATION COLUMNWHEREIN SAID DESENSITIZED STREAM IS SEPARATED INTO A GASEOUS FRACTIONSUBSTANTIALLY FREE OF KRYPTON AND XENON WHICH IS REMOVED AT THE TOP OFSAID COLUMN AND A SUBSTANTIALLY PURE KRYPTONXENON-OXYGEN LIQUID FRACTIONWHICH IS COLLECTED AT THE BOTTOM OF SAID COLUMN, CONDENSING VAPOR TOPRODUCE LIQUID REFLUX AT THE TOP OF SAID COLUMN BY INDIRECT HEAT